186 LOTS OF bolclt's scientific acquirements, as they are collected by Mm in " BZosmos/J we must omit Ms classification of Tolcanos into central and connected ones., especially as this system lias been introduced into science by other naturalists. We will return to Hximboldtfs pecxiliar field, and treat of Ms results on the creative and destructive volcanic power, in reference to mountains and rocks. TMs brings us to the extensive field of mineralogic geognosy, on which Humboldt always worked with great predilection with his old friend Leopold von Buchj and which treats of the formal composition and arrangement of the earth/s strata, and gradually leads to the geograpMcal form of its surface. The strata of the earth were to him the pages of a large book in which he read the events of the past; the kinds and forms of rocks he interpreted as the great characters of a history of creation extending over many thousands of years. He perceived the process of the formation of mountains as fourfold. He calls the matter wliich has once been projected from the interior of the earth in fluid masses, and which has now become more or less solid, eruption rock;—that matter wMch was contained in the fluid in small particles, and has been gradually precipitated, he calls sediment rock, and includes among it the greater part of the horizontal strata of earth, the so-called tertiary groups, which lie above the chalk formation, ^nd contain fossil remains of mammalia, Crustacea, &c. The transformed rocks are those changed by contact with volcanic or precipitated earth, or by vaporous exhalation or absorption of matters from below, while by conglomerates he means the sand and rock formation composed of mechanically-separated masses of the three other classes. All these four spe- cies Humboldt describes; as still progressing in their formation, the action of fire and water, though not so violent as formerly, is still exercising its influence. Among the first class, the eruption rock, Humboldt includes granite and Syenite,* the quartz porphyries, * A mixture of feldspar and homblend, called after the town of Syene, in Upper Egypt.